1. Field of the Invention
The present invention relates to guiding a magnetic flux. More particularly, the invention relates to guiding a magnetic flux using an electrically conducting conduit that has at least one electrically insulating gap that prevents the conduit from having a closed electrical path that links any closed path of the desired magnetic flux.
2. Background Information
The use of permeable magnetic cores to guide magnetic flux from one region to another in an electrical transformer is known. The term xe2x80x9cmagnetic fluxxe2x80x9d refers to the aggregate magnetic induction B passing through an open mathematical surface bounded by a closed path. A conventional electrical transformer 100 is illustrated in FIG. 1. The conventional electrical transformer 100 comprises a permeable magnetic core 101, such as iron, a primary electrical winding 103 that surrounds a first portion of the core 101 and a secondary winding 105 that surrounds a second portion of the core 101. When an alternating current is applied to the primary winding 103, a time-varying magnetic flux is produced, which passes through a region bounded by the primary winding 103. This magnetic flux is guided by the magnetic core 101 through a region bounded by the secondary winding 105. The time-varying magnetic flux thus guided to the interior region of the secondary winding 105 produces an alternating current in the secondary winding according to the mutual inductance between the primary winding 103 and the secondary winding 105.
While permeable magnetic cores in transformers are generally effective in guiding magnetic flux from a primary winding to a secondary winding, such magnetic cores suffer from some disadvantages. For example, magnetic cores can support a magnetic flux only up to the saturation magnetization of the magnetic material from which the core is made. Magnetic cores also suffer from hysteresis and eddy-current core loss. Moreover, conventional magnetic cores are non-linear (B does not vary linearly with H), and magnetic cores are heavy.
The use of electrical shields, such as in coaxial cables, in microwave cavities, in xe2x80x9cIF cansxe2x80x9d (intermediate frequency tuned transformers used in superheterodyne radios) and in shielded loop antennas, is also known. Such shields comprise an electrically conductive shell that surrounds a volume to be shielded. However, such shields are not capable of guiding a magnetic flux to pass through a region bounded by the shield.
Applicant has recognized a need for an approach for guiding a magnetic flux that does not suffer from the above-noted disadvantages associated with permeable magnetic cores of conventional transformers. The present invention fulfills this and other needs. The present invention is useful, for example, in electrical transformers and can be used to provide desired (e.g., intense) magnetic fields in measurement apparatuses that measure properties of a substance in the presence of an applied magnetic field. However, the present invention is not limited to these uses.
According to one aspect of the invention, there is provided a magnetic flux guiding apparatus. The apparatus comprises a conduit having a wall that comprises an electrically conducting material. An electrically insulating gap is formed in the wall along an entire length of the conduit. The insulating gap prevents the conduit from having a closed electrical path that links any closed path of the desired magnetic flux. For example, the insulating gap can prevent the conduit from having a closed electrical path that surrounds a lengthwise axis of the conduit. The apparatus also comprises a magnetic-field source disposed in proximity to the conduit. The magnetic-field source is configured to produce a magnetic flux that passes through an interior region bounded by the conduit.
In another aspect of the invention there is provided a method of making a magnetic-flux conduit. The method comprises identifying one or more mathematical surfaces through which leakage of magnetic flux is to be prevented and providing an electrically conducting material that conforms to the mathematical surfaces. Moreover, the method comprises providing an electrically insulating gap in the electrically conducting material such that no closed electrical path of the electrically conducting material links any closed path of the desired magnetic flux. The electrically insulating gap can be configured to prevent the conduit from having a closed electrical path that surrounds a lengthwise axis of the conduit.
In another aspect of the invention, there is provided another method of making a magnetic-flux conduit. The method comprises identifying one or more mathematical surfaces that surround a region through which a magnetic flux is to be directed wherein the surfaces are surfaces through which leakage of the magnetic flux is to be prevented. The method further comprises providing an electrically conducting material that encloses said one or more surfaces and providing an electrically insulating gap in the electrically conducting material that prevents the electrically conducting material from having a closed electrical path that links any closed path of the desired magnetic flux. The electrically insulating gap can be configured to prevent the conduit from having a closed electrical path that surrounds a lengthwise axis of the conduit.
In another aspect of the invention, there is provided a method of providing a magnetic flux. The method comprises providing a conduit having a wall that comprises an electrically conducting material, wherein an electrically insulating gap is formed in the wall along an entire length of the conduit. The electrically insulating gap prevents the conduit from having a closed electrical path that links any closed path of the desired magnetic flux. The electrically insulating gap can be configured to prevent the conduit from having a closed electrical path that surrounds a lengthwise axis of the conduit. The method further comprises providing a magnetic-field source in proximity to the conduit, and operating the magnetic-field source to produce a magnetic flux that passes through an interior region bounded by the conduit.
In another aspect of the invention, there is provided an electrical transformer. The transformer comprises a conduit having a wall that comprises an electrically conducting material, wherein an electrically insulating gap is formed in the wall along an entire length of the conduit. The electrically insulating gap can prevent the conduit from having a closed electrical path that surrounds a lengthwise axis of the conduit. In addition, the electrically insulating gap can prevent the conduit from having a closed electrical path that links any closed path of the magnetic flux produced by the primary winding. The transformer also comprises a primary electrical winding that surrounds a first portion of the conduit and a secondary electrical winding that surrounds a second portion of the conduit. The conduit can be configured in an overall toroidal shape or in a linear shape with two opposing open ends.
In the above-noted aspects, the conduit can be hollow, or, alternatively, can be filled with an electrically insulating material, such as a thermoplastic resin, for example. As another alternative, one or more permeable magnetic cores can be disposed within the conduit such that the magnetic cores do not electrically short the electrically insulating gap of the conduit. Where the conduit comprises a conventional electrically conducting material, the magnetic-field source can be a source of time-varying magnetic flux, such as an electrical coil. Where the conduit comprises an electrically superconducting material, the magnetic-field source can be a source of time-varying magnetic flux or constant magnetic flux, such as a permanent magnet.
In addition, the conduit can be configured such that the magnetic-field source is disposed in proximity to a first portion of the conduit having a first interior cross-sectional area and such that a second portion of the conduit has a second interior cross-sectional area that is smaller than the first interior cross-sectional area. In this manner, the conduit can focus the magnetic flux at the second portion. For example, the interior region bounded by the conduit can have a tapered shape, such as a conically tapered shape, located between the first portion and the second portion. An end of the tapered section can be configured in proximity to an end of the conduit.
It should be emphasized that the terms xe2x80x9ccomprisesxe2x80x9d and xe2x80x9ccomprisingxe2x80x9d, when used in this specification, are taken to specify the presence of stated features, integers, steps or components; but the use of these terms does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.